Molding apparatus

ABSTRACT

An improved apparatus for molding thermosetting material, such as strips of uncured mill rubber or other thermosetting elastomers, includes a preheater assembly which preheats the thermosetting material to a temperature which is below its curing temperature. A movable pot receives at least a portion of a charge of the preheated strip material at a loading station. The pot is then moved to a discharge or unloading station where a ram assembly is extended to force the thermosetting material from the pot into a mold. The ram assembly is then retracted and the pot is returned to the loading station. The pot is then filled so as to contain a charge which includes both preheated strip material and thermosetting material which was not forced into the mold on the previous cycle of operation. The pot is cooled at the loading station to maintain thermosetting material in the pot at a temperature below its curing or setting temperature. As the pot is being loaded, a slide block applies pressure against the mold and heats the thermosetting material in the mold to a temperature above its setting temperature.

[451 Sept. 17, 1974 MOLDING APPARATUS [76] Inventor: Don A. Taylor, 216Mill St.,

Wadsworth, Ohio 44281 22 Filed: May 11, 1973 21 Appl. No.1 359,600

Related US. Application Data [62] Division of Ser. No. 167,240, July 29,1971, Pat. Nov

[52] US. Cl... 425/251, 425/DIG. 51, 425/DIG. 228 [51] llnt. Cl 82% 5/04[58] Field of Search 425/250, 251, DIG. 228, 425/DIG. 51; 249/110 [56]References Cited UNITED STATES PATENTS 422,221 2/1890 Jayne 249/110 X2,415,961 2/1947 Nast 425/250 X 2,587,070 2/1952 Spillman 249/1102,883,704 4/1959 Jurgeleit 425/250 X 2,900,663 8/1959 Linhorst 425/DIG.228

3,021,568 2/1962 Scott, Jr 425/250 X 3,321,806 5/1967 Beebee 425/250 X3,327,355 6/1967 Corlin 425/250 3,764,248 10/1973 Hall 425/251 FOREIGNPATENTS OR APPLICATIONS 994,417 11/1951 France 425/DIG. 51

Primary Examiner-J. Spencer Overholser Assistant Examiner-Ronald J.Shore [5 7 ABSTRACT An improved apparatus for molding thermosettingmaterial, such as strips of uncured mill rubber or other thermosettingelastomers, includes a preheater assembly which preheats thethermosetting material to a temperature which is below its curingtemperature. A movable pot receives at least a portion of a charge ofthe preheated strip material at a 1oading station. The pot is then movedto a discharge or unloading station where a ram assembly is extended toforce the thermosetting material from the pot into a mold. The ramassembly is then retracted and the pot is returned to the loadingstation. The pot is then filled so as to contain a charge which includesboth preheated strip material and thermosetting material which was notforced into the mold on the previous cycle of operation. The pot iscooled at the loading station to maintain thermosetting material in thepot at a temperature below its curing or setting temperature. As the potis being .loaded, a slide block applies pressure against the mold andheats the thermosetting material in the mold to a temperature above itssetting temperature.

2 Claims, 14 Drawing Figures PAIENIEOSEP I 71914 SHKET 6 OF 7 MOLDIINGAPPARATUS This is a division, of application Ser. No. 167,240, filedJuly 29, 1971 now US. Pat. No. 3,748,075.

The present invention relates to an improved apparatus and method forforming articles of a thermosetting material.

There are three types of molding machines which are in frequentcommercial use, namely a compression press or machine, a transfer pressor machine, and an injection press or machine. When rubber or plasticarticles are made with a compression press, non-cured blanks formed of apredetermined volume of thermosetting material are loaded into cavitiesin a mold which is then subjected to heat and pressure for a timesufficient to set, i.e., cure, the thermosetting material. This moldingmethod has a number of advantages, including relatively low cost of thepress and molds and a high level of efficiency and dependability sincethe press is nonautomated. The drawbacks of the compression moldingprocess include relatively high labor operating costs, long cureperiods, and a relatively high material waste factor.

Transfer molding machines or presses have the advantage that parts canbe molded with relatively little flash material. This is possible due tothe fact that the molds in the press can be clamped tightly togetherbefore the transfer of material into the mold. Another advantage of thetransfer molding press or machine is that it has a relatively low laborcost in that a blank of thermosetting material can be loaded into a potinstead of being precut and manually placed in a mold cavity as is thecase with a compression molding press. However, transfer molding hassubstantial disadvantages in that there are relatively high labor costsinvolved in the preparation of the blanks of raw material for the press.In addition, there is a relatively high material waste or scrap factordue to the fact that the material is relatively cold when it isintroduced into a relatively hot mold cavity' which may result inpremature curing or setting of a skin surface. Another disadvantage oftransfer molding is that the required cure period is relatively long dueto the fact that the thermosetting material is introduced into the moldat a relatively low temperature.

Injection molding machines differ from compression and transfer moldingpresses in that the material is preheated and injected under highpressure into a mold cavity. This enables injection molding machines toovercome many of the disadvantages associated with compression andtransfer molding. However, injection molding machines have a relativelylarge waste or scrap factor due to a curing of material in anon-reuseable runner system. Another disadvantage of the injectionmolding machines is the inability, for certain articles at least, todesign a runner and gate system that will efficiently feed the moldcavity in a uniform manner. Another disadvantage of injection moldingmachines is the limit on material capacity which can be injected on anoperating cycle due to the poor ability of rubber and otherthermosetting materials to absorb or conduct heat necessitating theprovision of a relatively large reserve of preheated material which maycure prematurely.

Accordingly, it is an object of this invention to provide a new andimproved apparatus and method for molding elastomeric materials whichprovide the advantages of compression, transfer, and injection typemolding machines without the disadvantages which are associated withthese machines and, more specifically, to provide molding apparatus andmethod which with a minimum of waste can utilize relatively low cost rawmaterial which has not been pre-processed or formed into blanks andwhich include the use of a relatively inexpensive mold which does nothave a complicated runner and gate feeding arrangement.

Another object of this invention is to provide a new and improvedapparatus for molding thermosetting material where the apparatus isrelatively simple in construction and lends itself to repetitive qualityoperation with a minimum of supervision and waste.

Another object of this invention is to provide a new and improvedapparatus for forming molded articles from strip material wherein theapparatus includes a preheater assembly for preheating the stripmaterial, a pot for receiving a charge of the preheated strip material,and a ram or similar means for pressurizing a charge in the pot to forceat least a portion of the charge to flow from the pot into the mold.

Another object of this invention is to provide a new and improvedapparatus for molding a thermosetting material and wherein the apparatusincludes a mold assembly formed by a plurality of relatively movableparts and having an entrance opening to a mold cavity, a movable pot forholding a charge of the thermosetting material, an assembly for movingthis pot between a loading position and an unloading position on whichthe pot is effective to retain the parts of the mold assembly againstmovement and material can be forced from the pot into the mold cavity,wherein a device is provided for applying heat and pressure to the moldassembly upon movement of the pot: from the unloading position to theloading position to retain the parts of the mold assembly againstmovement relative to'each other and to promote a setting, i.e., curing,of the thermosetting material in the mold assembly.

Another object of this invention is to provide a cyclically operableapparatus for forming molded articles from a thermosetting material andwherein the apparatus includes a pot for holding a charge of thethermosetting material, a loader assembly for loading at least a portionof a charge of the thermosetting material into the pot during eachoperating cycle of the apparatus, and a control assembly for detectingwhen the portion of a charge remaining in the pot at the end of onecycle of operation of the apparatus and the thermosetting material addedto the pot during a next succeeding cycle of operation of the apparatusequals a charge of a predetermined magnitude and for interruptingoperation of the loader assembly in response to the detecting of acharge of the predetermined magnitude in the pot.

Another object of this invention is to provide a new and improvedapparatus for use in molding thermosetting material and wherein theapparatus includes a pot for holding a charge of the thermosettingmaterial and a cooling assembly at a pot loading station for maintainingthermosetting material in the pot at a temperature below the settingtemperature of the thermosetting material.

Another object of this invention is to provide a new and improved methodof fonning molded articles from thermosetting strip material wherein themethod includes the steps of providing a strip of thermosettingmaterial, preheating at least a portion of the strip of thermosettingmaterial to a temperature below its setting temperature, loading acharge of the preheated thermosetting strip material into a pot, andforcing at least a portion of this charge to flow from the pot into amold.

Another object of this invention is to provide a new and improved methodof molding thermosetting material and wherein the method includes thesteps of providing a mold assembly, providing a pot which is movablebetween a loading position at which the thermosetting material is placedinto the pot and an unloading position at which the thermosettingmaterial is forced to flow from the pot into the mold assembly, andwherein pressure is applied to the mold assembly after movement of thepot to the loading position.

Another object of this invention is to provide a new and improved methodfor molding thermosetting material during a plurality of operatingcycles wherein the method includes the steps of providing a pot, loadingthe pot with at least a portion of a predetermined charge of thethermosetting material during each of a plurality of operating cycles,forcing a portion of the predetermined charge of the thermosettingmaterial to flow into the mold and retaining another portion of thepredetermined charge in the pot during each of the plurality ofoperating cycles, detecting during a loading of a pot when the retainedportion of a charge remaining in the pot at the end of one of theoperating cycles and the thermosetting material added to the pot duringthe loading of the pot on the next succeeding operating cycle equals thecharge of predetermined magnitude, and interrupting the loading of thepot during each of the operating cycles upon detection of a charge ofthe predetermined magnitude in the pot.

These and other objects and features of the invention will become moreapparent upon a consideration of the following description taken inconnection with the accompanying drawings, wherein:

FIG. 1 is a partially broken away schematic illustration of a moldingapparatus constructed in accordance with the present invention;

FIG. 2 is a fragmentary schematic illustration taken generally along theline 22 of FIG. 1 and further illustrating the construction of themolding apparatus;

FIG. 3 is an enlarged fragmentary sectional view, taken generally alongthe line 3-3 of FIG. 2, illustrating the construction of a preheaterassembly for preheating strip material;

FIG. 4 is a fragmentary plan view, taken generally along the line 4-4 ofFIG. 1, further illustrating the construction of the preheater assembly;

FIG. 5 is an enlarged fragmentary schematic elevational view, takengenerally along the line 5-5 of FIG. 2, illustrating the relationshipbetween a movable pot, loading assembly, mold, slide block for heatingand applying pressure to the mold, and fixed and movable rams of themolding apparatus of FIG. 1;

FIG. 6 is a fragmentary schematic elevational view, similar to FIG. 5,of the loading of strip material into the pot by the loading assembly asthe pot is cooled;

FIG. 7 is a fragmentary schematic elevational view depicting the forcingof material from the pot into the mold;

FIG. 8 is a schematic fragmentary elevational view, similar to FIG. 7,depicting the pot after a major portion of a charge has been forced fromthe pot and a minor portion of a charge remains in the pot;

FIG. 9 is a fragmentary plan view, taken generally along the line 99 ofFIG. 1, illustrating the arrangement of a plurality of dischargeopenings in the bottom of the pot;

FIG. 10 is an enlarged fragmentary schematic view illustrating theforcing of material through the discharge openings in the pot and intothe mold;

FIG. 11 is a schematic fragmentary elevational view, depicting movementof the pot from the unloading position of FIGS. 7 and 8 toward theloading position of FIG. 5 with a minor or remaining portion of a chargein the pot;

FIG. 12 is an enlarged fragmentary view, generally similar to FIG. 10,illustrating the relationship between the mold and the pot upon initialmovement of the pot toward the loading position;

FIG. 13 is a schematic elevational view, generally similar to FIGS. 5and 11, depicting the application of heat and pressure to the mold bythe slide block during loading of the pot; and

FIG. 14 (on sheet two of the drawings) is a schematic sectional view,taken generally along the line 1414 of FIG. 1, illustrating therelationship between a guide rail and the slide block.

Although a molding apparatus 20 constructed in accordance with thepresent invention can be utilized to mold many different types ofmaterials, it is illustrated in FIG. 1 in association with athermosetting strip material 22 which is supplied from a suitablecontainer 24. The thermosetting strip material 22 is preheated to atemperature which is below its setting, i.e., curing, temperature in apreheater assembly 28 (see FIGS. 1-4). The preheated strip material isthen conducted to a loading station 30 where a loader assembly 32 loadsthe strip material into a movable pct 34 (FIGS. 5 and 6).

When the movable pot 34 has been filled so as to contain a predeterminedcharge of the thermosetting material 22, the pot 34 is shifted from theloading station 30 to an unloading or discharge station 38 where the potoverlies a mold 40 disposed on a movable ram 42 (FIG. 1). The movableram 42 and mold 40 are then raised so that a fixed ram 46 telescopicallyenters the pot 34 (FIG. 7) to force a major portion of the thermosettingmaterial in the pot 34 into the mold 40. The movable ram 42 is thenretracted (FIG. 8) and the pot 34 is shifted from the loading station 38to the unloading station 30 (FIG. 11) with a minor portion 50 of thethermosetting material remaining in the pot 34 to form.

an initial portion of a charge for a next succeeding cycle of operationof the molding apparatus 20.

After the pot 34 has returned to the loading station 30, the movable ram42 is again raised to press a horizontally extending bottom surface 56of a slide block 58 and pot 34 against the mold 40 (FIG. 13). Thispressure holds upper and lower sections 62 and 64 of the mold tightlytogether so that the thermosetting material 22 does not leak out betweenthe relatively movable sections of the mold. As the mold sections 62 and64 are pressed together by the slide block 58 and the next succeedingcharge of the thermosetting material is loaded into the pot 34, thethermosetting material in the mold sets. The curing of the material inthe mold 40 is promoted by heater elements 74 disposed in passages 76 inthe slide block 58. Since the pot 34 is also formed in the slide block58, a cooling block or element 80 is provided at the loading station 30to prevent the minor portion of the previous charge remaining in the pot34 from being heated to a temperature above its setting temperature asadditional thermosetting material is loaded into the pot.

Although it is contemplated that the molding apparatus will be utilizedto mold articles from strips of many different types of syntheticelastomers which are advantageously set with the application of heat,the molding apparatus 20 is advantageously utilized to mold articlesfrom a strip 22 of uncured mill rubber. It should be noted that thestrip 22 of raw mill rubber is utilized without being formed into blanksof a predetermined size, as is commonly done for compression andtransfer molding, or being formed into a cylinder or pellets, as isoften done for extrusion molding. Of course, this lack of processing ofthe strip rubber 22 before it is supplied to the molding apparatus 20substantially reduces the material cost for the articles molded by theapparatus.

To reduce the curing time required to set the articles molded from thestrip material 22 to their permanent configuration in the mold 48, thestrip material 22 is heated to a temperature which is slightly below itssetting (i.e., curing) temperature in the preheater assembly 28. Topromote a rapid heating of the strip material 22 so that adequatematerial is available to provide a relatively large charge for immediateloading into the pot 34 during successive cycles of operation of themolding apparatus 20, the preheater assembly 28 includes a pair ofheating platens 82 and 84 (FIG. 3). The platens 82 and 84 are pressedagainst opposite sides 86 and 88 of the strip material 22 under theinfluence of piston and cylinder assemblies 90 (see FIGS. 1 and 2).Thus, the heater platen 84 is connected with piston rods 94 (see FIGS. 3and 4) and is movable toward and away from the fixed heater platen 82 bythe piston and cylinder assemblies 98.

When a portion of the elastomeric strip material 22 to be heated isdisposed between the platens 82 and 84 (as shown in FIG. 3), the pistonand cylinder assemblies 90 are activated to press the platen 84 towardthe platen 82. This results in a firm pressure contact between heatingsurfaces 98 and INN) (FIG. 3) of the platens 82 and 84 and the oppositesurfaces 86 and 88 of the strip material 22 to promote the conduction ofheat from the platens to the strip material. Heater cores I84 and 106are provided in the platens 82 and 84. While it is contemplated thatmany different types of heating apparatus could be used, in theembodiment of the invention illustrated in FIG. 3, the cores T04 and1106 include electrical heating strips llltl and 1112.

Once a length of strip material 22 disposed between the heater surfaces98 and 1168 of the platens 82 and 84 has been preheated to the desiredtemperature, the piston and cylinder assemblies 90 are deactivated torelease the pressure applied to the strip material. Conveyor chains M6and I118 on the platens 82 and 84 are then driven by sprockets 122 tomove pivotally interconnected links I24 of the conveyor chains and feedthe heated portion of the strip material 22 to a storage loop 130 (FIG.II). The preheated strip material remains in the storage loop I until itis fed by rollers I32 and 1134 to the loader assembly 32 as requiredduring the loading of the pot 34. To maintain the material in thestorage loop 1130 at its preheated temperature, walls I38 (see FIG. 3)of the preheater assembly 28 are insulated so that the interior of thehousing is at substantially the preheat temperature. The conveyor chains1116 and 1118 are driven by a motor 142 (FIG. 4) which is connected witha feed roll I44 which is in turn connected with the sprockets 122 forthe conveyors I16 and H8 by a chain I48. Although the platens 82 and 84include conveyor chains I16 and 1118 having links with flat hardsurfaces which apply pressure against both sides of the strip material22, it should be understood that other types of heating and conveyingdevices could be provided in the preheater assembly 28 if desired.

A charge comprising a predetermined volume of the strip material 22 isaccumulated in the pot 34 during each cycle of operation of the moldingapparatus 20. This charge includes the minor portion 50 (see FIG. 41) ofthe charge remaining in the pot from the last cycle of operation of themolding apparatus 20 and preheated strip material 22 added during thepresent cycle of operation of the molding apparatus. Thus, at thebeginning of each cycle of operation of the molding apparatus 20, thepot 34 is returned to the loading station 38 with the remaining portion50 of the last charge in the pot 34. A sufficient quantity of the stripmaterial 22 is then deposited in the pot 34 by operation of the loaderassembly 32 to accumulate a charge of a predetermined magnitude.

In the illustrated embodiment of the invention, the loader assembly 32includes a movable ram I60 (see FIG. 5) which is extended telescopicallyinto the pot 34 with a length of the strip material 22 overlying the pot34 (FIG. 6). As the movable ram enters the pot 34, the portion of thestrip material 22 overlying the pot is severed and compressed into theother material in the pot. The ram 164) is then withdrawn from the potand the strip materisl 22 is advanced by the feed rollers 132 and I34 sothat a next succeeding portion of the strip material overlies the pot.The movable ram 160 is then lowered into the pot to again sever the endportion of the strip material 22 and compress the severed end portioninto the material previously deposited in the pot 34. It should be notedthat the pressure with which the movable ram compresses the material inthe pot 34 is sufficient to cause the strip material to flow againstside surfaces of the pot so that the pot is completely filled ahead ofthe ram I60 when it is in the lowered position of FIG. 6.

When the minor portion of the material remaining in the pot 34 from thepreceeding cycle of operation of the molding apparatus 28 and the stripmaterial deposited in the pot by operation of the loader assembly 32during the present cycle of operation of the molding apparatus 20 isequal to a charge of a predetermined magnitude, an actuator member I66on the ram 160 will not be moved downwardly past an actuator 168 for alimit switch 170 to signal a suitable control circuit that the desiredcharge has been accumulated in the pot 34. Although the limit switch 170has been shown schematically in FIGS. 5 and 6, it should be understoodthat the limit switch could be activated by the accumulation of apredetermined amount of material in the pot 34 or by movement of a drivepiston for the ram 160. In any case, the position of the switch actuatorI68 is adjustable to enable charges of different sizes to be accumulatedin the pot 34 and articles of different sizes to be molded.

If the minor or remaining portion 50 of the previous charge is heated toa temperature above its curing temperature for a substantial period oftime, or is scorched, this material cannot be used on the nextsucceeding cycle of operation of the molding apparatus 20 and is wasted.This remaining or minor portion 50 of the preceeding charge may beheated excessively by being momentarily exposed to a relatively hightemperature while the major portion of the previous charge is beingforced into the mold 40. The remaining or minor portion 50 of the chargecould be heated excessively under the influence of heat transferred fromthe heating element 74 in the slide block 58 as the material in the mold40 is cured and the pot 34 is loaded. Accordingly, the bottom surface 56of the pot 34 rests on the cooling element or block 80 having coils 172through which a suitable refrigerant is circulated (see FIGS. and 6). Byusing the cooling element 80, a substantial reduction in waste materialis achieved over a known molding device.

While it is important to provide the cooling element or block 80 toprevent the material in the pot 34 from being overheated, it is alsodesirable to maintain the material in the pot at a temperature closelyapproximating the preheat temperature. Accordingly, auxiliary heaters174 and 176 are proviced in the slide block 58 to maintain the materialin the pot 34 at substantially the preheat temperature. Suitable sensingdevices are associated with the auxiliary heaters 174 and 176 and thecooling element 80 to detect the temperature of the material in the potand regulate the operation of the cooling element and auxiliary heatersso that the material is neither cooled to too low a temperature orheated to too high a temperature.

After a charge of a predetermined magnitude has been loaded into the pot34 and the articles molded on the previous cycle of operation have beenremoved from the mold 40, the pot is shifted from the loading station 30to the unloading station 38. At the unloading station 38, dischargeopenings 184 in a bottom plate 186 (see FIG. 9) of the pot 34 arealigned with entrance passages or sprews 190 leading to mold cavities192 (FIG. 10). Since the discharge openings 184 in the bottom plate 186of the pot 34 are aligned with the entrance passages 190 to the moldcavities 192, a major portion of the charge in the pot 34 can be forcedthrough the discharge openings and entrance passages into the moldcavities when the lower ram 42 is raised and the fixed ram 46 enters thepot 34 (see FIGS. 7 and 10). The bottom plate 186 is removable to enablea bottom plate (not shown) having a different number and arrangement ofdischarge openings to be substituted for the bottom plate 186. Thisenables existing molds having sprue passage arrangements which aredifferent from that of the mold 40 to be utilized.

After the major portion of the charge in the pot 34 has been forcedthrough the discharge openings 184 into the mold 40, the movable ram 42is lowered so that the slide block 58 is clear of the fixed ram 46 (seeFIG. 8). The slide block 58 is then moved tothe right (as viewed in FIG.8) through the intermediate position of FIG. 11 to the loading positionof FIG. 13 with the minor portion 50 of the charge remaining in the pot34. Upon initial movement of the pot 34 toward the loading position,thermosetting material extending between the mold passages 190 and thedischarge openings 184 is severed in the manner illustrated in FIG. 12.As the bottom 56 of the pot 34 is moved relative to the mold 40, thepassages 190 to the mold cavities 192 are sealed by the bottom surface56 of the slide block 58 (FIG. 5) which moves over the mold 40.

During movement of the pot 34 toward the loading station 30, a scraperblade 198 (see FIG. 11) engages the bottom surface 56 of the slide blockand scrapes any material protruding out of the passages 184 from thebottom of the slide block 58. If desired, a movable knife blade could beprovided between the slide block 58 and the mold 40 to sever thematerial extending from the pot discharge passages 184 to the moldpassages 190. Of course, this knife blade would scrape away any materialadhering to the bottom of the slide block 58.

The slide block 58 may be moved relative to the loading and unloadingstations 30 and 38 by means of a mechanically actuated piston andcylinder assembly 204 (see FIGS. 1 and 2). When the piston and cylinderassembly 204 is retracted, a piston rod 206 (FIG. 2) moves the slideblock 58 toward the left (as viewed in FIG. 2) to move the pot 34 fromthe loading position to the unloading position. This movement of theslide block 58 is guided by a pair of parallel rails 208 and 210 whichare disposed on opposite sides of the molding machine (see FIG. 2) andextend for substantially the entire length of the molding machine. Tooperatively interconnect the guide rail 210 and slide block 58, a plate214 (FIG. 14) mounted on the guide rail extends into a groove 216 formedin the slide block 58. Of course, the guide rail 208 is connected withthe slide block 58 in a similar manner.

When the movable ram 42 and mold 40 are raised, the slide block 58 andpot 34 are also raised (see FIGS. 11 and 13). To enable the slide block58 to move upwardly with the movable ram 42, the guide rails 208 and 210are movably connected with a fixed frame 220 (FIG. 1) of the moldingapparatus 20 by vertical support bars 222 which are slidably received insleeves 224 connected to the frame. Therefore, upon upward movement ofthe movable ram 42, the support bars 222 slide upwardly relative to thesleeves 224. Adjustable stop nuts 226 are connected with the supportbars 222 to limit the downward movement of the guard rails 208 and 210upon retraction of the movable ram 42. To maintain the bottom surface 58of the pot 34 in contact with the cooling block while pressure is beingapplied to the mold 40 by slide block 58, the cooling block extendsbetween and is connected to the guide rails 208 and 210.

Once the thermosetting material in the mold cavities 192 and passageshas set, the excess material remaining in the mold passages 190 must bestripped away from the article in the mold cavity. To facilitateremoving this excess material, a pair of plates 230 and 232 (see FIG.10) are provided between the upper mold section 62 and the slide block58. The plate 230 is hingedly connected with the plate 232 so that itcan be reaised and moved away from the plate 232 after the mold 40 hasbeen moved out from under the slide block 58. Upon raising the plate230, sprue material 236 in the passages 190 is readily accessible andcan be removed from the lowr plate 232 by pulling upwardly on a thinsheet 240 of flash material which extends between the sprews associatedwith the openings 190 to the mold cavities 192. 4

To minimize waste material, the plates 230 and 232 limit the formationof the flash sheet 240 to a relatively small predetermined thickness. Byproviding a predetermined thickness and extent of the flash sheet 240,the waste material in the flash can be minimized while still providingsufficient strength to enable the sprew material 236 to be stripped fromthe mold 40. To provide for a flash sheet of a predetermined thickness,a flat thin cavity 24-4 is formed between parallel surfaces 246 and 248of the plates 230 and 232. These surfaces form the flash 24a of the samethickness and extent during each molding operation so that the amount offlash and waste material can be minimized while still providingsufficient flash to enable the sprue material 236 to be stripped fromthe mold.

Under certain operating conditions it is contemplated that the mold 40will be moved transversely outwardly from between the fixed and movablerams 42 and 46. However, under other operating conditions it iscontemplated that it may be desirable to lower the movable ram 42 tosuch an extent that the mold 40 can be opened while remaining on themovable ram. If the mold 4-0 is to be opened while remaining on themovable ram 22, a relatively large clearance must be provided betweenthe mold 40 and the slide block 5% when the movable ram 42 is fullyretracted. To provide for this relatively large clearance, the frame llincludes a support section 250 (see FIG. l) which is movable from theoperating position shown in solid lines in FIG. 1 to the operatingposition shown in dashed lines in FIG. l. The fixed ram 4-6 is securedto the frame section 250 so that upon movement of the frame section tothe dashed lineposition of FIG. l, a relatively large clearance isprovided between the fixed ram 46 and movable ram 42. To enable theframe section 250 to be moved to the dashed line position, the framesection is connected to support columns or posts 254 having threadedupper end portions by means of releasable lower clamp sections (notshown) and nuts 256. Of course, if the frame section 250 could bereleasably connected to the support post 254!- in any desired manner.

From the foregoing description, it can be seen that the moldingapparatus 20 combines the advantages of compression, transfer andinjection type molding without the disadvantages which are frequentlyassociated with these machines. Thus, elastomeric strip material 22,such as rubber, can be molded in relatively inexpensive molds with aminimum of waste without the provision of a relatively complicated sprueand gate arrangement which is difficult to feed. The molding apparatus29 can be operated at a relatively high speed since the strip material22 is quickly heated in the preheater 23 and transferred to the pot 34while material which was forced into the mold M on the previous cycle ofoperation is being cured. To minimize waste material, a relatively smallor minor portion 50 of a charge from one cycle of operation forms a partof the charge for the next cycle of operation of the molding apparatus.To prevent this remaining material from being overheated, a coolingblock 80 cools the pot 34 while it is being loaded with preheated stripmaterial by operation of the lower assembly 32. The minimization ofwaste is also promoted by the mold assembly M) which includes plates 239and 232 for providing flash 240 of a predetermined thickness on eachcycle of operation of the molding apparatus. Relatively high. speedeconomic operations of the molding apparatus 20 is also promoted by theslide block 58 which applies heat and pressure to the mold 410 while thepot 34 is being charged with the preheated strip material 22.

Having described a specific preferred embodiment of the invention, thefollowing is claimed:

ll. An apparatus comprising a mold body having first and second moldsections which at least partially define a plurality of mold cavities,said first mold section including surface means for defining inner endportions of a plurality of spaced apart sprue passages connected incommunication with said mold cavities, a movable pot for receiving acharge of material, said pot including a bottom wall defining aplurality of outlet passages and being movable between a loadingposition disposed to one side of said mold body and an unloadingposition in which said outlet passages are aligned with said spruepassages, flash limiter means for forming a thin sheet of flash materialof a predetermined thickness interconnecting and circumscribing saidsprue passages, said flash limiter means including a first platedisposed in abutting engagement with said bottom wall of said pot whensaid pot is in said unloading position, said first plate includingsurface means for defining a plurality of spaced apart outer endportions of said sprue passages, said outer end portions of said spruepassages being disposed in alignment with said outlet passages in saidbottom wall of said pot when said pot is in said unloading position,said flash limiter means further including a second plate connected withsaid first plate and disposed in abutting engagement with said firstmold section, said second plate including surface means for definingintermediate portions of said sprue passages, said intermediate portionsof said sprue passages being disposed in alignment with said inner andouter end portions of said sprue passages, said first and second platesincluding first and second parallel surface means spaced a predetermineddistance apart and extending between said sprue passages for defining athin flash chamber extending between and circumscribing each of saidsprue passages, and ram means cooperating with said pot when it is inthe unloading; position for forcing a charge of material to flow fromsaid pot through said outlet openings into said sprue passages and fromsaid sprue passages into said mold cavities and flash chamber to formarticles in the mold cavities having projecting sprue portionsinterconnected by a thin sheet of flash material.

2. An apparatus as set forth in claim 1 further including drive meansfor moving said pot from said unloading position to said loadingposition and for simultaneously therewith sliding said bottom wall ofsaid pot along said first plate to move said outlet passages out ofalignment with said sprue passages and to at least partially block saidsprue passages with said bottom wall of said pot duirng a portion of themovement of said pot from the unloading position to the loadingposition.

1. An apparatus comprising a mold body having first and second moldsections which at least partially define a plurality of mold cavities,said first mold section including surface means for defining inner endportions of a plurality of spaced apart sprue passages connected incommunication with said mold cavities, a movable pot for receiving acharge of material, said pot including a bottom wall defining aplurality of outlet passages and being movable between a loadingposition disposed to one side of said mold body and an unloadingposition in which said outlet passages are aligned with said spruepassages, flash limiter means for forming a thin sheet of flash materialof a predetermined thickness interconnecting and circumscribing saidsprue passages, said flash limiter means including a first platedisposed in abutting engagement with said bottom wall of said pot whensaid pot is in said unloading position, said first plate includingsurface means for defining a plurality of spaced apart outer endportions of said sprue passages, said outer end portions of said spruepassages being disposed in alignment with said outlet passages in saidbottom wall of said pot when said pot is in said unloading position,said flash limiter means further including a second plate connected withsaid first plate and disposed in abutting engagement with said firstmold section, said second plate including surface means for definingintermediate portions of said sprue passages, said intermediate portionsof said sprue passages being disposed in alignment with said inner andouter end portions of said sprue passages, said first and second platesincluding first and second parallel surface means spaced a predetermineddistance apart and extending between said sprue passages for defining athin flash chamber extending between and circumscribing each of saidsprue passages, and ram means cooperating with said pot when it is inthe unloading position for forcing a charge of material to flow fromsaid pot through said outlet openings into said sprue passages and fromsaid sprue passages into said mold cavities and flash chamber to formarticles in the mold cavities having projecting sprue portionsinterconnected by a thin sheet of flash material.
 2. An apparatus as setforth in claim 1 further including drive means for moving said pot fromsaid unloading position to said loading position and for simultaneouslytherewith sliding said bottom wall of said pot along said first plate tomove said outlet passages out of alignment with said sprue passages andto at least partially block said sprue passages with said bottom wall ofsaid pot duirng a portion of the movement of said pot from the unloadingposition to the loading position.